Optical multi-demultiplexer

Abstract

An arrayed-waveguide grating type optical multi-demultiplexer includes input waveguides, a first slab waveguide, a channel waveguide array, a second slab waveguide, and output waveguides. A pair of different refractive index regions, each having a refractive index different from that of the second slab waveguide, are formed on the second slab waveguide near a boundary between the second slab waveguide and channel waveguide array. The different refractive index regions project in peninsular shapes from both side portions of the slab waveguide. Light traveling from each waveguide of the channel waveguide array toward the output waveguides passes through the different refractive index regions. An optical distribution with a flattened field-distribution peak is created at a boundary between the second slab waveguide and output waveguides.

1. An optical multi-demultiplexer comprising:
 a substrate; 
 input waveguides formed on the substrate; 
 a channel waveguide array including a plurality of curved waveguides arranged such that optical path lengths of adjacent ones of the curved waveguides are gradually increased from an inside toward an outside of a curved configuration of the curved waveguides; 
 output waveguides formed on the substrate; 
 a first slab waveguide formed between the input waveguides and the channel waveguide array; 
 a second slab waveguide formed between the channel waveguide array and the output waveguides, and 
 a different refractive index region formed at a position close to the channel waveguide array within the second slab waveguide, the different refractive index region having a lower refractive index than a core of the second slab waveguide, the different refractive index region extending in a direction in which the waveguides of the channel waveguide array are arranged, and 
 the different refractive index region having a tapered shape decreasing in width from both side portions toward a central portion of the second slab waveguide. 
 
   
   
     2. The optical multi-demultiplexer according to  claim 1 , wherein the different refractive index region has a refractive index equal to a refractive index of a clad layer of the second slab waveguide. 
   
   
     3. The optical multi-demultiplexer according to  claim 1 , wherein the different refractive index region comprises a pair of peninsular different refractive index regions projecting from both sides of the second slab waveguide toward a central portion of the second slab waveguide. 
   
   
     4. The optical multi-demultiplexer according to  claim 1 , wherein the different refractive index region is spaced apart from each of both sides of the second slab waveguide. 
   
   
     5. The optical multi-demultiplexer according to  claim 1 , wherein the different refractive index region has a width varying in a direction in which the waveguides of the channel waveguide array are arranged. 
   
   
     6. The optical multi-demultiplexer according to  claim 1 , wherein the different refractive index region has a refractive index varying in a direction in which the waveguides of the channel waveguide array are arranged. 
   
   
     7. The optical multi-demultiplexer according to  claim 1 , wherein island regions having a refractive index different from each of the first and second slab waveguides are formed, in addition to the different refractive index region, on at least one of a position close to the channel waveguide array within the first slab waveguide and a position close to the channel waveguide array within the second slab waveguide. 
   
   
     8. An optical multi-demultiplexer comprising:
 a substrate; 
 input waveguides formed on the substrate; 
 a channel waveguide array including a plurality of curved waveguides arranged such that optical path lengths of adjacent ones of the curved waveguides are gradually increased from an inside toward an outside of a curved configuration of the curved waveguides; 
 output waveguides formed on the substrate; 
 a first slab waveguide formed between the input waveguides and the channel waveguide array; 
 a second slab waveguide formed between the channel waveguide array and the output waveguides, and 
 a different refractive index region formed at a position close to the channel waveguide array within the second slab waveguide, the different refractive index region having a higher refractive index than a core of the second slab waveguide, the different refractive index region extending in a direction in which the waveguides of the channel waveguide array are arranged, and 
 the different refractive index region having a reverse-tapered shape increasing in width from both side portions toward a central portion of the second slab waveguide. 
 
   
   
     9. An optical multi-demultiplexer comprising:
 a substrate; 
 input waveguides formed on the substrate; 
 a channel waveguide array including a plurality of curved waveguides arranged such that optical path lengths of adjacent ones of the curved waveguides are gradually increased from an inside toward an outside of a curved configuration of the curved waveguides; 
 output waveguides formed on the substrate; 
 a first slab waveguide formed between the input waveguides and the channel waveguide array; 
 a second slab waveguide formed between the channel waveguide array and the output waveguides, and 
 a different refractive index region formed at a position close to the channel waveguide array within the second slab waveguide, the different refractive index region having a higher refractive index than a core of the second slab waveguide, the different refractive index region extending in a direction in which the waveguides of the channel waveguide array are arranged, 
 wherein the different refractive index region comprises a pair of peninsular different refractive index regions projecting from both sides of the second slab waveguide toward a central portion of the second slab waveguide.